All Courses
Explore Courses UPSC Exam UPSC Test Series Free Notes EduRev Infinity Get the App Login Join for Free
Sign in Open App
Computer Science Engineering (CSE) Exam  >  Computer Science Engineering (CSE) Questions  >  A disk has 200 tracks (numbered 0 through 199... Start Learning for Free
SaveJoin the Discussion on the App
A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previous request, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)
  • a)
    2 and 3
  • b)
    3 and 3
  • c)
    3 and 4
  • d)
    4 and 4
Correct answer is option 'C'. Can you explain this answer?
FREE This question is part of
Download PDF Attempt Test
Download PDF Attempt this Test
Verified Answer
A disk has 200 tracks (numbered 0 through 199). At a given time, it wa...
According to Shortest Seek Time First: 90-> 120-> 115-> 110-> 130-> 80-> 70-> 30-> 25-> 20 Change of direction(Total 3); 120->15; 110->130; 130->80 According to First Come First Serve: 90-> 120-> 30-> 70-> 115-> 130-> 110-> 80-> 20-> 25 Change of direction(Total 4); 120->30; 30->70; 130->110;20->25 Therefore,Answer is C
View all questions of this test
Most Upvoted Answer
A disk has 200 tracks (numbered 0 through 199). At a given time, it wa...
Explanation:
To determine the number of times the head changes its direction for the SSTF and FCFS disk scheduling policies, we need to analyze the order in which the pending requests are serviced.

SSTF (Shortest Seek Time First):
1. Start at track 120.
2. The nearest pending request is track 115 (5 tracks away).
3. Move the head to track 115.
4. The nearest pending request is track 110 (5 tracks away).
5. Move the head to track 110.
6. The nearest pending request is track 130 (20 tracks away).
7. Move the head to track 130.
8. The nearest pending request is track 130 (0 tracks away).
9. Move the head to track 130.
10. The nearest pending request is track 70 (60 tracks away).
11. Move the head to track 70.
12. The nearest pending request is track 80 (10 tracks away).
13. Move the head to track 80.
14. The nearest pending request is track 90 (10 tracks away).
15. Move the head to track 90.
16. The nearest pending request is track 30 (60 tracks away).
17. Move the head to track 30.
18. The nearest pending request is track 25 (5 tracks away).
19. Move the head to track 25.
20. The nearest pending request is track 20 (5 tracks away).
21. Move the head to track 20.

FCFS (First Come First Serve):
1. Start at track 120.
2. Service the pending request for track 30.
3. Move the head to track 30.
4. Service the pending request for track 70.
5. Move the head to track 70.
6. Service the pending request for track 115.
7. Move the head to track 115.
8. Service the pending request for track 130.
9. Move the head to track 130.
10. Service the pending request for track 110.
11. Move the head to track 110.
12. Service the pending request for track 80.
13. Move the head to track 80.
14. Service the pending request for track 20.
15. Move the head to track 20.
16. Service the pending request for track 25.

The head changes its direction whenever it moves from a higher track number to a lower track number or vice versa.

Number of times the head changes its direction for SSTF: 2 times (from track 120 to 115, and from track 115 to 110)

Number of times the head changes its direction for FCFS: 4 times (from track 120 to 30, from track 30 to 70, from track 70 to 115, and from track 115 to 130)

Therefore, the correct answer is option 'C': 3 times for SSTF and 4 times for FCFS.
< Previous Question Next Question >
Explore Courses for Computer Science Engineering (CSE) exam

Similar Computer Science Engineering (CSE) Doubts

Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2], [180, 134, 1], [60, 20, 0], [212, 86, 3], [56, 116, 2], [118, 16, 1] Currently head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is ______ .Note -This was Numerical Type question.

Consider a storage disk with 4 platters (numbered as 0, 1, 2 and 3), 200 cylinders (numbered as 0, 1, … , 199), and 256 sectors per track (numbered as 0, 1, … , 255). The following 6 disk requests of the form [sector number, cylinder number, platter number] are received by the disk controller at the same time: [120, 72, 2] , [180, 134, 1] , [60, 20, 0] , [212, 86, 3] , [56, 116, 2] , [118, 16, 1] Currently the head is positioned at sector number 100 of cylinder 80, and is moving towards higher cylinder numbers. The average power dissipation in moving the head over 100 cylinders is 20 milliwatts and for reversing the direction of the head movement once is 15 milliwatts. Power dissipation associated with rotational latency and switching of head between different platters is negligible. The total power consumption in milliwatts to satisfy all of the above disk requests using the Shortest Seek Time First disk scheduling algorithm is _______. Correct answer is '85'. Can you explain this answer?

Top Courses for Computer Science Engineering (CSE)View all

Top Courses for Computer Science Engineering (CSE)

A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer?
Question Description
A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? for Computer Science Engineering (CSE) 2024 is part of Computer Science Engineering (CSE) preparation. The Question and answers have been prepared according to the Computer Science Engineering (CSE) exam syllabus. Information about A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? covers all topics & solutions for Computer Science Engineering (CSE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer?.
Solutions for A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? in English & in Hindi are available as part of our courses for Computer Science Engineering (CSE). Download more important topics, notes, lectures and mock test series for Computer Science Engineering (CSE) Exam by signing up for free.
Here you can find the meaning of A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer?, a detailed solution for A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? has been provided alongside types of A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice A disk has 200 tracks (numbered 0 through 199). At a given time, it was servicing the request of reading data from track 120, and at the previousrequest, service was for track 90. The pending requests (in order of their arrival) are for track numbers. 30 70 115 130 110 80 20 25. How many times will the head change its direction for the disk scheduling policies SSTF(Shortest Seek Time First) and FCFS (First Come Fist Serve)a)2 and 3b)3 and 3c)3 and 4d)4 and 4Correct answer is option 'C'. Can you explain this answer? tests, examples and also practice Computer Science Engineering (CSE) tests.
Explore Courses for Computer Science Engineering (CSE) exam

Top Courses for Computer Science Engineering (CSE)

Explore Courses

Suggested Free Tests

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Get App
© EduRev
Education Revolution
Signup to see your scores go up within 7 days!
Access 1000+ FREE Docs, Videos and Tests
Takes less than 10 seconds to signup